Telecinema system using electroluminescent diodes

Abstract

A cinematographic film to be reproduced by television is driven at constant speed in synchronism with the sweep cycle of one or more camera tubes each positioned to pick up images projected upon a receiving surface thereof whose luminous persistence equals at least a sweep cycle. The film is periodically transluminated, during the retrace phase of the scanning beam, by a light pulse emitted by an electroluminescent diode -- or by a cluster of such diodes operating on different wavelengths -- defining a quasi-pinpoint light source, the diode being excited by an energizing pulse whose length does not exceed the duration of a line scan of the camera tube.

What we claim is: 
     
       1. A telecinema system comprising: photoelectric transducer means including at least one camera tube provided with a receiving surface;   lens means in line with said camera tube for projecting images of a cinematographic film onto said receiving surface, said tube being provided with sweep means for scanning the projected images in a recurrent raster of line and frame scans with successive sweep cycles separated by intervening retrace intervals;   a quasi-pinpoint light source including at least one electroluminescent diode positioned in line with said lens means for transluminating said film;   constant-speed drive means for said film synchronized with said sweep means; and   a generator of energizing pulses for said diode connected to said sweep means for triggering during said retrace intervals, said energizing pulses having a length not exceeding the duration of a line scan, said receiving surface having a luminous persistence lasting for at least a sweep cycle.   
     
     
       2. A telecinema system as defined in claim 1 wherein said sweep means produces a generally sawtooth-shaped voltage pulse with a leading edge followed by a plateau, said generator being provided with differentiation means for detecting said leading edge to trigger the emission of an energizing pulse. 
     
     
       3. A telecinema system as defined in claim 2 wherein a sweep cycle encompasses a pair of interlaced frames, said generator including frequency-dividing means in cascade with said differentiation means for making only every other voltage pulse effective to trigger the emission of an energizing pulse. 
     
     
       4. A telecinema system as defined in claim 1 wherein said light source comprises a cluster of electroluminescent diodes energizable by said generator for emitting light pulses of different wavelengths.